Inability of Laplace's law to estimate sub-bandage pressures after applying a compressive bandage: a clinical study

Objective: The aim of the current study was to compare pressures exerted on the lower limb by a high compression bandage as recorded by sub-bandage sensors and those estimated by Laplace's law. The correlation between pressures obtained in each anatomical zone and the corresponding limb perimeters were explored. Method: For the measurement of sub-bandage pressures, four anatomical zones in the lower right limb were determined. Pressures were recorded by nine pneumatic sensors and a PicoPress transducer. A two-layer compression bandage system (UrgoK2, Urgo Group, France) was used for the dressing. Pressures were registered in supine position. Sensor pressures were compared with those estimated by a modified Laplace's equation. Results: A total of 47 female volunteers were recruited (mean age: 21.9±2.3 years) to the study. In the four anatomical segments studied, pressures obtained by the sensors were lower than would be expected by applying Laplace's law (p<0.05). The biggest difference between the two methods was found at the supramalleolar level (42.1% lower by sensors compared with Laplace's equation). The correlation coefficient between pressure recorded by the sensors and that calculated at the perimeters was very weak, ranging from 0.5233 to 0.9634. Conclusion: Laplace's law, used to predict the sub-bandage pressure after applying a compressive bandage in the lower limb, was not useful, providing significantly higher pressures than those obtained by pneumatic sensors. Laplace's law underestimates the variable musculoskeletal components at the different segments of lower limb that act as compression damping forces.